The Romans started by learning what the Greeks
thought about medicine, and in fact most Roman doctors were from
Greece, or of Greek origin. Like the Greeks, the Romans believed in
the four humors and the power of bloodletting. The most important Roman
doctor was Galen (GAY-lenn), who lived in the 100s AD and wrote a book about medicine. Galen's book about medicine (actually
a shortened version of it) was the main medical book that doctors used
in Europe for the next thousand years and more.
Galen repeated a lot of Hippocrates' work on the four humors, but he also added a lot of observations about how the human body worked that he learned from looking at the insides of human bodies. He saw the insides of people by looking at wounded soldiers and gladiators. And he cut open a lot of animals to see how they worked. Galen certainly knew more about anatomy than Hippocrates did. Galen understood that the heart pushed blood around the body, for instance. But he thought that air entered the blood within the heart, instead of in the lungs. Galen knew that nerves controlled the movement of the body, and that people thought with their brains. But Galen did not make any real advances in treating people. He still thought that blood-letting was a good idea.